You should put a valve on the hot water line so that you can flush the tank without washing crud into it. One on the cold intake side isn't so useful, but with one, you could remove the tank without turning off the entire house water, and it's cheap enough to do. I use full flow ball valves.

It is incredibly dangerous and absolutely against code to have a shut-off on both the inlet and outlet of a hot water heater. If both are closed, the WH relies completely on the proper functioning of the PRV to deal with pressure/expansion changes and faults if the heater is left on.

If the PRV fails, then we start to see explosions of the type some of you post links to on this site every now and again.

My neighbor has valves on both the inlet and outlet of his WH and I live in fear. Say he shuts them both off and forgets and the PRV fails?

Shut-offs on WHs should only be installed on the cold side. That way, the fixtures and fittings (think washer hoses) of the hot supply will also take the strain of any increase in pressure should the PRV fail and there is fault with the WH. There is therefore less chance of a boom.

Regarding my statement that the valve one the "cold side wasn't as important etc.. My bad!! I certainly meant the valve on the HOT side was not as important as on the intake (cold) side. Thanks to HJ for catching my error!

Think of it this way in regards to the water heater being a bomb if the inlet and outlet were shut off and the TPV failed
- how is this different than if the inlet were shutoff and no other hot water fixture in the house was turned on? It's still a closed system.

I have checked and it would not appear to be against code everywhere, as I originally assumed. Sorry. In Illinois for example it appears to be allowed.

But I maintain that it is dumb to have two shut-offs on a WH. If you the plumber have put a ball valve on the hot you have opened the door for human nature to injure someone.

They possibly would not want to call a plumber when the T+P is working properly and releasing water.
They put a cap on the T+P "I can fix this honey"...
The heater builds up excessive pressure and pinholes a weld on the tank...
They close both valves and know it is now time to call you to replace the heater...
You pull up to a house with a bunch of emergency vehicles in front of it because the homeowner never turned off the gas,"It wasn't what was leaking"
With hot open maybe they will have a chance blowing a water supply.

Yes, there might be exceptions. From my 365+ days of plumbing experience as a fully qualified and master homeowner, I would guess that on a residential 2 heater parallel installation, installing a hot and cold on each heater might be essential. When 1 heater takes a dump, that heater can be isolated, and the other heater will work without the leaker leaking.

But I maintain that traditionally a 1 tank residential heater will only have a cold water valve.

A tankless might require both a cold and hot shut off with bypass valves to allow for flushing though.

It is not against code to add a shut off on the hot water side and it makes it easier to service the equipment. The TPR valve is what protects the equipment. If you don't have one and all of the hot water fixtures are in the off position, it is no different than having a valve installed on the hot side and in the closed position.

I understand your concern and appreciate your passion but you are incorrect.

I think you need to specify the code that prohibits this, otherwise you are misleading people with false information.

A shutoff valve is required on the cold water side per the IPC and IRC. In the IPC it can be found in 503.1 and in the IRC it is in P2903.9.2

I have supplied you with direct references, now I ask the same from you.

You cannot fix stupid and keep people from injuring themselves due to their own negligence. It is bad enough that we have to have stickers on lawn mowers telling people that they are not hedge trimmers because some moron picked up a mower to trim his hedges and won a lawsuit.

Under normal operating conditions, the valves will be in the open position.

Again, as long as you don't have water running in the house, there is no difference between that and a closed valve on the hot side. Either way the water is restricted and pressure can build up, hence the need for a TPR valve.

If you are stupid enough to cap the TPR, leave the gas on and turn off both valves then you don't belong in society anyway.

If you don't like it then don't do it in your house. It is not required but it certainly is not against any nationally recognized codes.

I guess I am just be one of those weirdos who likes to see installations done as per the manufacturer's installation instructions, which never show a hot-side shut off valve for a traditional single tank installation.

I'm with jar on this one. I don't see how a closed faucet or shower head is any different from a closed valve. I guess Ian is suggesting that a soldered copper elbow is a weaker connection than a valve and would burst before the tank would as opposed to a ball valve not bursting in a high pressure situation. This may or may not be correct, but I can't imagine a huge difference in strenght between the two.

Also, I believe a bigger concern would be to have threads on the bottom a T&P extension pipe, where a unfamiliar homeowner would even have the ability to cap it. Absolutely no threads allowed on the bottom of that pipe.

A hot water side valve would allow you to change the water heater without having to drain all the hot water lines.